Topographical models of geographical areas may be used for many applications. For example, topographical models may be used in flight simulators and for planning military missions. Furthermore, topographical models of man-made structures (e.g., cities) may be extremely helpful in applications such as cellular antenna placement, urban planning, disaster preparedness and analysis, and mapping, for example.
Various types and methods for making topographical models are presently being used. One common topographical model is the digital elevation map (DEM). A DEM is a sampled matrix representation of a geographical area which may be generated in an automated fashion by a computer. In a DEM, coordinate points are made to correspond with a height value. DEMs are typically used for modeling terrain where the transitions between different elevations (e.g., valleys, mountains, etc.) are generally smooth from one to a next. That is, DEMs typically model terrain as a plurality of curved surfaces and any discontinuities therebetween are thus “smoothed” over. Thus, in a typical DEM no distinct objects are present on the terrain.
One particularly advantageous 3D site modeling product is RealSite® from the present Assignee Harris Corp. RealSite® may be used to register overlapping images of a geographical area of interest, and extract high resolution DEMs using stereo and nadir view techniques. RealSite® provides a semi-automated process for making three-dimensional (3D) topographical models of geographical areas, including cities, which have accurate textures and structure boundaries. Moreover, RealSite® models are geospatially accurate. That is, the location of any given point within the model corresponds to an actual location in the geographical area with very high accuracy. The data used to generate RealSite® models may include aerial and satellite photography, electro-optical, infrared, and light detection and ranging (LIDAR).
Another advantageous approach for generating 3D site models is set forth in U.S. Pat. No. 6,654,690 to Rahmes et al., which is also assigned to the present Assignee and is hereby incorporated herein in its entirety by reference. This patent discloses an automated method for making a topographical model of an area including terrain and buildings thereon based upon randomly spaced data of elevation versus position. The method includes processing the randomly spaced data to generate gridded data of elevation versus position conforming to a predetermined position grid, processing the gridded data to distinguish building data from terrain data, and performing polygon extraction for the building data to make the topographical model of the area including terrain and buildings thereon.
Nonetheless, topographical models are no longer reserved for advanced modeling systems such as those discussed above. Various Internet service providers such as Google™ and Microsoft® are looking to provide access to 3D topographical models over the Internet that show users how a city or location appears in as much realism as possible. This may advantageously help increase a user's awareness of a given area and provide an exploratory environment. Such companies are striving to provide environments that are easier to use, more realistic and ultimately more useful. Improving the user experience involves increasing the quality of the 3D environment in terms of better terrain, more highly detailed city/building models, and higher resolution imagery of the terrain and buildings.
However, one significant challenge is that, while the terrain and models are quite small in terms of their geometries or structure, the imagery and textures used to enhance the basic models are typically very large. Over a highspeed network, such as that found within most corporate networks, downloading models and textures from a local network server is relatively fast and therefore not particularly problematic. Over the Internet, however, downloading these quantities of data can be extremely slow and significantly diminish user experience because of the relatively limited bandwidth available.
Currently, several network-enabled 3D viewers exist that permit users to view models from a network or Internet server. These viewers include Google™ Earth, Microsoft® VirtualEarth, and NASA WorldWind. All viewers share the ability to view untextured building models with some varying degree of textured terrain. Textured models tend to be very rudimentary. Microsoft® VirtualEarth attempts to apply textures over their models, but the delay can be so long as to become unacceptable to users.
Various approaches have been developed for remotely accessing terrain data. One example is set forth in U.S. Pat. No. 6,496,189 to Yaron et al. This patent discloses a method of providing data blocks describing three-dimensional terrain to a renderer. The data blocks belong to a hierarchical structure which includes blocks at a plurality of different resolution layers. The method includes receiving from the renderer one or more coordinates in the terrain along with indication of a respective resolution layer, providing the renderer with a first data block which includes data corresponding to the coordinate(s) from a local memory, and downloading from a remote server one or more additional data blocks which include data corresponding to the coordinate(s) if the provided block from the local memory is not at the indicated resolution layer. Despite the existence of such approaches, further advancements may be desirable for remotely retrieving and displaying large amounts of geospatial data.